In a post to the Microsoft Security Response Center blog on Wednesday evening, Christopher Budd, an MSRC security program manager, wrote, "I wanted to let you know that we've just posted an Advance Notification for an out-of-band bulletin release. We plan to release one Windows security bulletin with a maximum severity of Critical; scheduled for a target time of 10 a.m. PT on Thursday Oct. 23, 2008. A restart will be required."
Microsoft typically releases Security Bulletins on the second Tuesday of every month, an event that has come to be known as Patch Tuesday. On rare occasions, as it last did in April 2007, Microsoft will issue an "out-of-band bulletin" to address vulnerabilities that require immediate attention.
The most recent Patch Tuesday was Oct. 14, when Microsoft released 11 security bulletins to address four "critical," six "important," and one "moderate" vulnerabilities.
The out-of-band bulletin will address a vulnerability (or more than one) that is rated "critical" for Windows 2000, Windows Server 2003, and Windows XP. The vulnerability is rated "important" for Windows Vista and Windows Server 2008.
Microsoft plans to host a Webcast about its bulletin at 1 p.m. PDT Thursday. Those wishing to attend can visit the Microsoft TechNet registration page.
Microsoft has not yet provided any information about the vulnerability beyond stating that it could be used for remote code execution.